eli5, what did they do to plastic to make it recyclable ?
In: Chemistry
“Plastic” is a very broad term – it covers an entire group of materials (typically synthetic polymers), and is often misused.
As a general, though not fixed, rule, if you want to recycle (that is, return to original condition) then you have to be able to melt the plastic and reform it. “thermoplastics” is a term normally used for this. They have been around for 70+ years. Things like Coke bottles are an example of this material type.
As another broad category, “thermosetting plastics” are also used. These cant be melted down and reformed. Things like pens are typically thermopsetting plastics. But not being able to reform it doesn’t mean that it can’t be reused. They can be ground up and included within another material mix. These have also been around for decades
On top of that are a whole bunch of other polymers like polyamides (nylon variants) and microcellular materials (e.g. chloroprene) that can either be reused or recycled. Unsurprisingly, these are also not new materials.
So nothing has happened to make them recyclable, but mechanisms to collect and cost effectively recycle have become more available.
Whether plastic can be recycled or not, and how to do it, depends on the resin type you use to make it. There are many types such as PET, PVC, HDPE etc., that have different uses and different processes to recycle them.
First you need to sort the plastic waste into their various types, sometimes even into different qualities and purities. Then the plastic is cleaned and shredded. After that you melt it down and turn it into small granules (similar to what you find at artificial grass soccer fields, those little black bits of plastic). Manufacturers use the granules to make new products again, and the cycle continues.
There are many different types of plastic. Most plastic is almost all made from hydrocarbons (ie compounds of hydrogen and carbon) usually with some added stuff like dyes (for colors) or UV protection in very small amounts. For an ELI5, there are two broad categories – thermoset and thermoplastics. Plastic products are made by heating raw plastic materials, forming it into shape and then allowing it to cure.
Thermoset plastics undergo chemical changes during curing. This means the final product has a different compound compared to the raw plastic material. This makes it difficult to recycle. (think of this kind of plastic as bread – once you bake the bread you cannot make it back to the raw materials)
Thermoplastics, on the other hand, is like ice cream. During curing, the plastic hardens but it melts again when heated up. This usually make thermoplastics more easily recyclable.
In short, the don’t DO anything to plastics – some are just more easily recycled while others are more difficult.
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